1. Field of the Invention
This invention relates in general to an apparatus and a method for filling fuel. Hydrogen gas or compressed nature gas is filled as a fuel gas into an automobile.
2. Description of the Related Art
As a next generation automobile, compressed nature gas automobiles using compressed nature gas as the fuel gas and hydrogen gas automobiles using hydrogen gas as the fuel gas are developed. These automobiles are characterized in that discharge amount of carbon dioxide gas, nitrogen oxide (NOx), and oxysulfide (SOx), etc. is very little.
For refueling, these automobiles are the same as the gasoline automobile. These automobiles arrive at a supply base having a fuel filling apparatus (dispenser) for filling their fuel, i.e., the compressed nature gas or the hydrogen gas, and the compressed nature gas or the hydrogen gas are supplied from the fuel filling apparatus (for example, referring to non-patent document 1). In addition, the compressed nature gas and the hydrogen gas are generally referred to a fuel gas.
The conventional fuel Filling apparatus for the automobile, for example, comprises a fuel gas supplying path, a flow modulating valve, an integrating flowmeter, a shut-off valve, and an overfilling protective valve. The fuel gas supplying path is connected to a pressure accumulator that is used as a source for supplying a high-pressure fuel gas. The flow modulating valve modulates a supply amount of the fuel gas provided from the pressure accumulator. The integrating flowmeter is used to measure and integrate the flow of the fuel gas. The shut-off valve stops supplying the fuel gas when filling of the fuel gas is completed. The overfilling protective valve will shut off the supply path when the pressure of the fuel gas exceeds a preset pressure.
FIG. 14 is a schematic cross-sectional view illustrating an example of a conventional overfilling protective valve. The overfilling protective valve 120 includes a fuel gas path 121, a valve unit for opening and closing the fuel gas path 121 by a valve body 130, and a valve displacement means 123 for displacing the valve 130 based on a filling pressure of the fuel gas, referring to non-patent document 2.
In addition, the valve displacement means 123, in the conventional example, is a spring, and thus the following description is made by referring to the spring 123.
The fuel gas path 121 is connected to a fuel gas supply path 3. The valve unit 122 includes a valve rod 131 having the valve body and a valve box 131 with a sliding hole 132 where the valve rod 131 is slidably received therein. The sliding hole 132 is connected to the fuel gas path 121. The valve body 130 is formed at a location that is equivalent to a valve chest 134 formed in the sliding hole 132.
The spring 123 is received in a spring receiving unit 140, and the spring 123 obtains a repulsive force from the interior of the spring receiving 140 to provide a resilient force in the direction of the valve unit 122 to a piston 142 through a ball 141.
The piston 142 is received in a piston receiving unit 143.
The piston 142 is fixed on one end of the valve rod 131, so that the piston 142 and the valve rod move together. A branch path 144, which branches from the fuel gas supply path 3 at the secondary side of the overfilling protective valve 120, is connected to the piston receiving unit 143. The fuel gas within the fuel gas supply path 3 at the secondary side passes through the branch path 144, and then is supplied to between the valve unit 122 and the piston 142 in the piston receiving unit 143.
The overfilling protective valve 120 operates in the following manner.
When the pressure of the fuel gas flowing from the fuel gas supply path 3 at the secondary side to the lower side of the piston 142 in the piston receiving unit 143, i.e., the gas pressure at the secondary side, is lower than the preset pressure, the valve rod 131 moves downwards with respect to FIG. 4 due to the resilient force generated by the spring 123, and therefore, a gap is created between the valve body 130 and the inner wall of the fuel gas path 121. In this manner, the fuel gas path 121 is open, and then the fuel gas flows from the fuel gas supply path 3 at the primary side to the fuel gas supply path 3 at the secondary side.
As the gas pressure at the secondary side becomes the preset pressure, the piston 142 is moved by the gas pressure to press and compress the spring 123. Then, the fuel gas path 121 is closed by that the valve body 130 is in contact with the inner wall of the fuel gas path 121. In this manner, the fuel gas is stopped flowing from the fuel gas supply path 3 at the primary side to the fuel gas supply path 3 at the secondary side.
As described above, the overfilling protective valve 120 is constructed to switch the fuel gas path 121 on or off according to a balance between the gas pressure at the secondary side and the resilient force of the spring 123. In other words, the preset pressure for that the overfilling protective valve 120 is switched on or off is determined by the resilient force of the spring 123.
A fuel filling apparatus for the compressed nature gas is disclosed in the non-patent document 1. That document disclosed a fuel filling apparatus (a dispenser unit) having an overfilling protective device that is a valve for modulating a supply amount of nature gas.
Non-patent document 1: “TECHNICAL GUIDELINE OF STANDARD AND SAFETY FOR COMPRESSED NATURE GAS”, incorporated juridical body Japanese Gas Association, pp. 11, April.
Non-patent document 2: “HIGH PRESSURE REGULATOR”, IPROS Co. Ltd., Jun. 2, 1996.
However, the ordinary gas possesses a property that the gas temperature varies due to the Joule Thomson effect when the gas passes through a thin path, such as a valve. Specifically, similar to the other high pressure gas (such as inert gas, oxygen gas, etc.), the temperature of the compressed nature gas decreases obviously when the compressed nature gas expands adiabatically from its compressed status (for example, under a pressure of 20 MPa). In addition, the hydrogen gas, which is different from the ordinary gas, possesses property that the gas temperature rises due to the Joule Thomson effect. Therefore, the temperature of the hydrogen gas rises when the hydrogen gas passes through a valve, etc.
When the overfilling protective valve 120 is heated or cooled by the fuel gas that passes through the overfilling protective valve 120, the spring 123 is thus heated or cooled, so that the elastic coefficient of the spring changes. As a result, there will be a problem that the overfilling protective valve 120 fails to operate by the correct set pressure.
As a fuel tank for the automobile, a container made of Fiber Reinforced Polymer (FRP) for light weight is used. An upper limit of the temperature for using the FRP container is restricted in consideration its durability, and the upper limit is generally about 85° C.
As described above, similar to the other high pressure gas (such as inert gas, oxygen gas, etc.), the temperature of the compressed nature gas decreases due to the Joule Thomson effect when the compressed nature gas expands adiabatically from its compressed status (for example, under a pressure of 35 MPa). In consequence, the temperature of the compressed nature gas reduces when the compressed nature gas passes through a machine with thin holes or slits, such as a mechanical valve, a check valve, or a coupler.
Therefore, when the nature gas is filled into the fuel tank, since the gas temperature is very difficult to rise, the gas can be easily filled within a short time without managing the tank temperature.
On the other hand, the hydrogen gas, which is different from the ordinary gas, possesses a property that the gas temperature will rise due to the Joule Thomson effect. Therefore, the temperature of the hydrogen gas rises when the hydrogen gas passes through a machine, for example, a valve. Furthermore, when filling the hydrogen gas into the fuel tank, the temperature also rises due to the adiabatic compression, and therefore, the gas temperature rises easily to a very high value. Since the fuel tank made of FRP has an upper limit for the temperature, a serious temperature management is required during filling the hydrogen gas. Additionally, it is very difficult to increase the filling speed.
For the hydrogen gas automobile, for a purpose that the temperature of the fuel tank does not exceed a designed temperature, a method is disclosed to directly measure the temperature of the fuel tank while the gas is filled into the fuel tank.
More specifically, a method is provided that a temperature terminal (a temperature sensor) is set in the fuel tank of the automobile, wherein a fuel filling pipe is connected to the fuel tank of the automobile and wires for measuring the temperature are connected to the temperature terminal, so that the gas supply amount is modulated and the fuel is filled according to the detected tank temperature.
However, in the above method, it requires to connect an additional wire for measuring the temperature with the pipe for filling the fuel to the automobile, causing a problem of taking a lot of time in operation.
In addition, since a lower explosion concentration in the air is 4 vol % and the upper explosion concentration is 75 vol % for the hydrogen gas, it is very dangerous if the hydrogen gas leaks. Therefore, in general, parts used in the fuel filling apparatus for the hydrogen gas has to include a pressure-resistance and explosion-proof structure specified by JIS C 0931. Accordingly, it is quite expensive to make or maintain the management of the fuel filling apparatus for the hydrogen gas, so that there are problems of high price and large volume of the apparatus.